A stent is a generally longitudinal tubular device formed of biocompatible material, preferably a metallic or a plastic material, which is useful in the treatment of stenosis, strictures or aneurysms in body vessels such as blood vessels. It is well known to employ a stent for the treatment of diseases of various body vessels. The device is implanted either as a "permanent stent" within the vessel to reinforce collapsing, partially occluded, weakened or abnormally dilated sections of the vessel or as a "temporary stent" for providing therapeutic energy treatment to the diseased vessels. A permanent stent may need to be retracted if the stent is not placed at an appropriate site or for other reasons; therefore, it becomes a temporary stent. Stents are typically employed after angioplasty of a blood vessel to prevent restenosis of the diseased vessel. Stents may be useful in other body vessels such as the urological tract and bile duct. The temporary stent is defined in this invention as a stent that is expandable inside a vessel and retractable thereafter from the vessel of a patient.
Stents generally include an open flexible configuration. The stent configuration allows the stent to be configured in a radially compressed state for intraluminal catheter insertion to an appropriate site. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by an inflatable balloon attached to a catheter or the stent may be of the self-expanding type that will radially expand once deployed from the end portion of a delivery catheter. One stent example is U.S. Pat. No. 4,733,665 to Palmaz, which is incorporated herein by reference.
An expanded PTFE (ePTFE) vascular graft is well known to have a substantially non-thrombogenic fluorinated surface. An ePTFE patch is also used for repairing the ruptured blood vessel wall. An ePTFE graft and its process of making are well known to one who is skilled in the art.
U.S. Pat. No. 5,810,870 to Myers et al. discloses a stent covered by an ePTFE to take the advantage of the substantially non-thrombogenic properties of a fluorinated surface, wherein the ePTFE cover exhibits suitable expansion capabilities so as to enable the cover to expand upon expansion of the underlying stent. The ePTFE covered stent exposes the fluorinated ePTFE surface, not the stent surface, to the underlying tissue or the flowing blood stream. Occasionally, the ePTFE cover might shift itself from its associated stent because the ePTFE cover is loosely on the stent. This misalignment phenomenon of an ePTFE cover on a stent becomes a clinical problem when the stent is non-retractably deployed because the ePTFE cover does not firmly adhere to the stent structure. Said ePTFE covered stent also blocks the openness of the stent and does not allow blood to continuously provide nutrient to the tissue behind the implanted stent. Tissue necrosis might occur due to inadequate perfusion, especially for a long ePTFE-covered stent.
U.S. Pat. No. 4,632,842 to Karwoski et al., U.S. Pat. No. 4,718,907 to Karwoski et al., and U.S. Pat. No. 5,246,451 to Trescony et al. disclose one fluorine-containing coating technique for coating fluorine, fluoride, or fluorine-containing compound onto the surface of a substrate to have a very low surface energy and to be essentially non-thrombogenic. However, none of the above-referred patents teaches coating fluorine, fluoride, or fluorine-containing compounds onto a stent that has a very small stent material surface to open surface ratio. Other preferred techniques of depositing fluorine-containing material onto a stent include dipping, dip coating, pasting (or paste coating), and/or sintering processes.
Furthermore, Radiofrequency has been used to provide thermal energy to an "electrode", wherein the electrode is defined as a metallic element that contacts a tissue of a patient, such as a metallic stent in this invention. The radiofrequency energy is delivered from an active "electrode" to a tissue and returns from a dissipating electrode to the radiofrequency generator. The radiofrequency treatment exposes a patient to minimal side effects and risks. Radiofrequency energy, when coupled with a temperature control mechanism, can be supplied precisely to the apparatus-to-tissues contact site to obtain the desired temperature for treating a tissue.
A stent deployed within a vessel, such as a coronary stent, has excellent metal-to-tissue contact surface. It becomes an ideal medium for receiving thermal energy from the ablated tissue to the stent when a stent needs to be collapsed for whatever reasons using a shape-memory Nitinol electrode. RF energy can be applied to a surface fluorinated stent to render the stent less prone to restenosis, too.
Therefore, there is a first need for an improved tubular stent having radially expandable and retractable capabilities for emergency removal when there is a clinical requirement. Furthermore, there is a second clinical need to provide a surface fluorinated retractable stent or a retractable stent having its surface coated by fluorine-containing material while still preserve the openness of the stent configuration, such as a coil stent, a mesh stent, a scaffold stent, a sleeve stent, a porous stent, or a permeable stent.